The invention relates to a device for encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, wherein the bitstream of the source signal is divided into n-bit source words, which device comprises converting means adapted to convert said source words into corresponding m-bit channel words, the converting means being adapted to convert a block of p consecutive n-bit source words into a corresponding block of p consecutive m-bit channel words, such that the conversion for each block of p consecutive n-bit source words is substantially parity preserving, where n, m and p are integers, m&gt;n.gtoreq.1, p.gtoreq.1, and where p can vary. The invention also relates to a recording device comprising the encoding device, for recording the channel signal on a record carrier, to the record carrier itself, to an encoding method, and to a device for decoding a stream of data bits of a binary channel signal obtained by means of the encoding device, so as to obtain a stream of databits of a binary source signal.
An encoding device mentioned in the foregoing is known from U.S. Pat. No. 5,477,222 (PHN 14448). The document discloses a device for encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, satisfying a (1,8) runlength constraint. That means that, in a serial datastream of the channel signal at minimum one `zero` and at maximum eight `zeroes` are present between two consecutive `ones` in the channel signal. It should be noted in this respect that normally an additional preceding step, such as a 1T precoding, is applied to the (1,8) constrained sequence, resulting in a runlength limited sequence with minimum runlength 2 and maximum runlength 9.
The known conversion is parity preserving. `Parity preserving` means that the parity of the n-bit source words to be converted equal the parity (after modulo-2 addition) of the corresponding m-bit channel words into which they are converted. As a result, the n-to-m conversion device as claimed does not influence the polarity of the signal.
As the conversion is parity preserving, an efficient DC control can be applied, such as by inserting DC control bits in the datastream of the source words.